lix/corepkgs/nar.nix
Shea Levy 58204a3c39 corepkgs/nar.nix: Prefer local builds
nar.nix's builder depends on coreutils and nix itself being in $PATH.
Unfortunately, there's no good way to ensure that these packages exist
in the same place on the remote machine: The local machine may have nix
installed in /usr, and the remote machine in /usr/local, but the
generated nar.sh builder will refer to /usr and thus fail on the remote
machine. This ensures that nar.sh is run on the same machine that
instantiates it.

Signed-off-by: Shea Levy <shea@shealevy.com>
2013-08-14 22:32:41 +02:00

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with import <nix/config.nix>;
let
builder = builtins.toFile "nar.sh"
''
export PATH=${nixBinDir}:${coreutils}
if [ $compressionType = xz ]; then
ext=.xz
compressor="| ${xz} -9"
elif [ $compressionType = bzip2 ]; then
ext=.bz2
compressor="| ${bzip2}"
else
ext=
compressor=
fi
echo "packing $storePath..."
mkdir $out
dst=$out/tmp.nar$ext
set -o pipefail
eval "nix-store --dump \"$storePath\" $compressor > $dst"
hash=$(nix-hash --flat --type $hashAlgo --base32 $dst)
echo -n $hash > $out/nar-compressed-hash
mv $dst $out/$hash.nar$ext
'';
in
{ storePath, hashAlgo, compressionType }:
derivation {
name = "nar";
system = builtins.currentSystem;
builder = shell;
args = [ "-e" builder ];
inherit storePath hashAlgo compressionType;
# Don't build in a chroot because Nix's dependencies may not be there.
__noChroot = true;
# Remote machines may not have ${nixBinDir} or ${coreutils} in the same prefixes
preferLocalBuild = true;
}